General and special purpose host computers often include provisions for various peripheral functionality, such as a communications modem, memory expansion, or an add on hard disk drive. In order to facilitate the addition of various peripherals the Personal Computer Memory Card International Association (PCMCIA) has endeavored to standardize a family of peripheral cards with a requisite PCMCIA interface. The PCMCIA defined parameters can be found in the PC Card Standard Release 2.0 document, published by the PCMCIA, 1030B East Duane Avenue, Sunnyvale Calif. and incorporated herein by reference. The defined parameters include physical parameters such as dimensions, input/output connections such as control, address, and data buses, signal parameters such as operating levels, and impedances, power levels, source polarity and levels and certain operating procedures.
Based upon the provisions supported by the host computer for additional devices such as the PCMCIA devices it is generally known that PCMCIA peripheral cards draw their power from the host computer socket and are generally controlled by a single RESET line when inserted or removed from the host computer socket in order to reinstate functionality.
However, a new class of PCMCIA devices, such as wireless modems, and the like, available from manufacturers such as Motorola, Inc. at 1303 East Algonquin Road, Schaumburg, Ill. 60193, are designed to continue to operate while removed from the socket or while the socket and the host computer are powered-off. These PCMCIA devices have their own power source and CPU that allows each device to maintain independent functionality once removed from the host computer socket. This paradigm shift allow the users the enhanced capabilities of remaining logged into a network while removed from the host computer thus operating in a manner that allows them to maintain a partial communication link such as, for example storing messages until the peripheral card is reinserted into the host computer.
However since existing PCMCIA peripheral cards, are designed to function in accordance with the PCMCIA standard where the only power source and reset state is generated by the host computer, an undesirable phenomenon can occur. This phenomenon results in the circuitry on the peripheral cards being unnecessarily or inadvertently reset, thus interfering with the planned or expected functionality of the device.
Clearly a need exists for a peripheral function or card that has a PCMCIA compliant interface that is additionally capable of operating reliably in a deterministic fashion in an environment where the host device and peripheral device both contain their own CPU and power source.